The relationship between the criminal legal system and the mental health system has been an issue of longstanding debate. This debate has received a new impetus in recent months with challenges to the insanity defense itself. Most commonly, however, states which have reformed the insanity defense recently have not abolished it, but they have supplemented it with the possibility of a verdict of Guilty But Mentally Ill (GBMI). The movement toward adoption of GBMI statutes has been largely bereft of analysis of underlying empirical assumptions. The intent of the proposed investigation is to test these assumptions and to examine possible unintended side effects. Specifically, the investigation is directed toward the following objectives: (1) to identify the effects of a GBMI option on the number and characteristics of offenders accorded a special verdict; (2) to determine the effects of a GBMI option on the content and process of juror and jury decision making; (3) to analyze the ethical and legal problems presented by GBMI reforms in the light of evidence about underlying empirical assumptions. Two studies are proposed to address these objectives: (1) an experimental study of juror decision making in response to case vignettes; (2) a simulation of jury decision making in response to a videotaped reenacted trial under various conditions of verdict instructions. Results from each of these studies will be integrated with legal analyses in analyzing and reporting the data.